The present invention relates to a method for processing manure, fermented manure or waste water having a relatively high ammonia nitrogen concentration, said liquid manure being subjected to nitrification in a first step and to denitrification in a subsequent step, an aerated reactor which contains active sludge rich in nitrifying bacteria being used in the nitrification step and acid-neutralizing chemicals being added to said reactor if necessary and a continuously fed upflow sludge bed (USB) reactor which contains a very compact biomass which is capable of converting nitrate to nitrogen gas and to which an organic substrate is added for use in the denitrification step.
A method of this type is known from, inter alia, Agrarisch Dagblad of Mar. 14, 1988. With this method the liquid fraction of fermented semi-liquid manure is treated. The biologically degradable organic substances, nitrifiable nitrogen and phosphorus which are present in the liquid fraction of anaerobic or fermented semi-liquid manure can be largely removed. The method essentially consists in a coupling of a nitrification step in a nitrification reactor in which ammonia is converted by bacteria to oxidized nitrogen with a denitrification step in a denitrification reactor in which oxidized nitrogen is converted by bacteria to nitrogen gas, the phosphate present in the liquid being concentrated as a chemical precipitate in the reactor at the same time. Oxidation of ammonia results in lowering of the pH, which, with this method, can be countered by metering in lime and/or metering in effluent from the denitrification reactor (recycling) to the nitrification reactor. During the nitrification step of this method there will also be some removal of nitrogen and phosphate since the bacteria degrade biologically degradable substances which have passed through the fermentation to give CO.sub.2 and H.sub.2 O. The nitrogen and phosphorus thus liberated can be incorporated in the new cells of the active sludge. With this method the nitrification reactor (which can be either a fed batch reactor or a batch reactor) is operated batchwise. It is then aerated until all ammonia has been nitrified, after which the aeration is stopped temporarily in order to allow the sludge to settle. The nitrified liquid manure is run off for treatment in the denitrification step, while the active sludge remains behind in the nitrification reactor for a subsequent cycle. In the denitrification step the effluent from the nitrification reactor is pumped upwards through a USB (upflow sludge bed) reactor. In this reactor there is a very compact biomass which is capable of converting nitrate to nitrogen gas. In order to allow this step to proceed, an organic substrate--for example methanol--must be added to the reactor. Acid is consumed during the denitrification step, as a result of which the pH in the bacterial bed rises. As a consequence of this rise, an insoluble precipitate of phosphate, with the calcium ions present in the liquid, forms. The manure processing consisting of manure fermentation and separation of fermented manure, followed by the method for treatment of the liquid fraction of fermented semi-liquid manure, which has been described above, and is shown in FIG. 1.
A number of manure processing works are being developed at present, for example Promest in Helmond and Memon in Deventer. In these works semi-liquid manure is evaporated to give a dry product, which costs a great deal of energy since semi-liquid manure consists of more than 90% of water. Moreover, this evaporation is a complex technology which in fact still has to be developed for use on manure. The cost price of processing of this type for the formation of dry granular or powder manure is consequently very high.
An approach which differs from that described above is the treatment of semi-liquid manure in conventional effluent treatment installations. Currently this is also being used for treatment of liquid manure from calves. The conventional manure treatment has the significant disadvantages that the process produces a large amount of sludge (excess bacteria) and that the process is not capable of removing the phosphate. This means that extra provisions have to be made for sludge treatment and dephosphating. A conventional manure treatment also requires a fairly large amount of space.
This method, as reported in Agrarisch Dagblad of Mar. 17, 1988, has the advantage that it is relatively inexpensive and can be carried out in a compact installation. However, a number of problems also arise in this case in the treatment of fermented manure.
A compact manure treatment installation for manure and fermented manure or ammonium nitrogen containing waste water can be produced and maintained only if:
a) the metering of the fermented liquid fraction is matched to the nitrification capacity of the nitrification reactor. The nitrification reactor must not be overloaded but must also not operate underloaded. PA0 b) The metering of methanol (or other sources of carbon) to the denitrification reactor is matched to the nitrate load in the denitrification reactor. In the case of undermetering not all nitrate is removed; in the case of overmetering, however, methanol (or other source of carbon) is present in the effluent to be discharged. PA0 c) The effluent recycling from denitrification reactor to nitrification reactor is controlled such that it is optimal. Too little recycling leads to a nitrate concentration which has an inhibitory action on the bacteria; too much recycling has the consequence that the reactor is filled mainly with liquid which has already been treated. PA0 a) the loading of the nitrification reactor is controlled to obtain an optimum nitrification and denitrification, said optimum being obtained on the basis of the following data: PA0 b) the loading of the denitrification reactor is controlled to obtain an optimum denitrification, said optimum being obtained by: PA0 c) the temperature in both the nitrification reactor and the denitrification reactor is maintained below 40.degree. C. (preferably 25.degree. C.-35.degree. C.) and PA0 d) the pH-value in the nitrification reactor is maintained in the range of 6 to 8.5 (preferably 6.5-7.5).
Said points can be achieved by the use of separate instruments, it being necessary to carry out some of the diverse operations by hand. Moreover, the results of the various measurements cannot be integrated and translated into a control action without the intervention of one operator. Furthermore, the effluent from the nitrification reactor can still contain organic substances which cannot be further degraded in the nitrification reactor. Organic material which passes into the denitrification reactor can be converted into inorganic material in that reactor with the liberation of ammonium nitrogen which is then (insofar as it is not fed via the recycle stream) discharged with the effluent.